The present invention is directed to a circuit arrangement for digital setting of the gain of a digitally adjustable, adaptive receive amplifier independently of a reception signal. The circuit arrangement is used in a system having at least one control station and at least one secondary station that in a block-by-block transmission of binary coded data conforming to a data transmission method wherein a pulse signal 0 is allocated to one binary value of the binary coded data and a pulse signal that alternates in operational sign is allocated to another binary value.
During data transmission between two data stations, for example a control station and a secondary station in a data station system, transmitted data can be subject to attenuation distortion. The data incoming at the data station is therefore amplified before further processing to a level that corresponds to the optimum reception level of the data station. The degree of required amplification depends on the receiving data station, on the length of the data transmission link and on the load of the data transmission link caused by other data stations connected to the data transmission link. Methods are known in the prior art for determining appropriate gain factors in a program-controlled fashion after installation or after modification of the data station system. The factors are determined either once or after every activation of a secondary station. For example, the control station repeatedly transmits test data to the secondary stations for identifying the gain factor, these secondary stations modifying their reception gains in steps until a proper reception level is determined. In a further pass, the control station again repeatedly transmits test data to which the secondary stations then reply with a return signal, whereupon the control sets its reception gain in a step-by-step procedure. Finally, the respective gain factors are stored in the secondary stations, and the respective gain factors for a respective secondary station are stored in the control station, these gained factors to be respectively set before the data transmission to a secondary station.
For amplifying the reception signals, the data stations have digitally adjustable receive amplifiers whose gain factors are identified in a program-controlled fashion as set forth above in a separate time interval which requires a great amount of control. European Patent Application EP-A-0 171 643 (corresponding to U.S. Pat. No. 4,768,204) discloses a method and an apparatus for the transmission of signals between a control station and a plurality of secondary stations that have digitally adjustable receive amplifiers and that identify the gain factors in the described procedure during a learning phase that is separately executed. The time required to identify the gain factors is then lost for useful data transmission. Thus, the data transmission rate is reduced during this time.
Since only a data block having a previously known level can be reliably received by the data stations, a local record means, which is required for service purposes and that acquires all data blocks transmitted on a data transmission link having generally different signal levels as well as signal levels that are unknown to the local record means, cannot be realized.